Lapping machines, such as lapping machine 10 shown in FIG. 1, typically include at least a ring sprocket 16 having a lower lapping wheel 32 and a center sprocket 12. The ring sprocket 16 has a radius 18 and center sprocket 12 has a radius 14. During operation of lapping machine 10, center sprocket 12 rotates about a center axis 24. Teeth of a carrier 20 mesh with the teeth of ring sprocket 16 and the teeth of center sprocket 12 so that carrier 20 is urged into simultaneous rotational movement about its center axis 26 and planetary movement between radius 14 and radius 18. Carrier 20 includes one or more openings 22 for carrying a work piece 28, such as a disk that is exposed to lower lapping wheel 32 during operation. The diameter 30 of carrier 20 is a fixed distance, equal to the difference between radius 18 of ring sprocket 16 and radius 14 of center sprocket 12. By virtue of movement of carrier 20, work pieces 28 are subjected to abrasive contact with lower lapping wheel 32, ultimately forming planar surfaces on work pieces 28 having surfaces small discontinuities/variances in flatness. It is desirable to maintain extremely high surface tolerance control for proper function of the work pieces 28 used in semiconductors.
Over time, carriers are subject to wear, producing work pieces having unacceptably low levels of tolerance control, requiring replacement of the carriers. As a result, testing must be conducted that correlate work piece quality to the carriers used to produce the work pieces. Currently, an identification number is formed in or placed on each carrier requiring manual recordation of the carrier number for each lot or group of work pieces produced using a carrier. Manual recordation is time-consuming, prone to errors, and does not sufficiently isolate the carrier so as to identify a single “bad” opening, requiring possible premature disposal of a carrier.
What is needed is a carrier that is configured for testing as part of a work piece quality control system which does not require manual identification of the carrier, yet more quickly and more accurately identifies the carrier used to produce a given lot or group of work pieces.